Pittsford, N.Y. — The Bills can't afford many more injuries on the offensive line.

On Thursday, left guard Chris Williams walked off the field accompanied by a trainer after suffering a toe injury. He's just the latest Bills lineman to go down. Left tackle Cordy Glenn started off camp on the non-football illness list and hasn't been cleared to practice. Meanwhile, utility lineman Chris Hairston left practice on Wednesday with a back injury and didn't return on Thursday.

That left rookie Cyril Richardson at left guard with the first team at times with J.J. 'Unga also seeing some reps there. Rookie Seantrel Henderson is still the starting left tackle, meaning fifth and seventh-round rookies made up the left side of the Bills' offensive line on Thursday.

It's not an ideal situation to have during training camp when the offensive line should be starting to come together as a unit. But it's early, and quarterback EJ Manuel thinks the offensive line has responded well to the adversity.

"Those guys have done a great job, especially this week," Manuel said. "Picking up defenses blitzes, their looks. They're communicating very well at the line of scrimmage. That allows us to really pick it up.

"I'm happy, especially for those young guys. The more reps they get, the better they're going to be."

A few other observations from Thursday.

1. Sammy Watkins catches a long touchdown

The highlight of Bills practice on Thursday came early during 11-on-11 drills. The Bills were practicing being backed up against their own goal line. After trying a few runs up the middle, EJ Manuel dropped back and lofted a perfectly thrown pass down the left sideline, and guess who was on the other end? Sammy Watkins, of course. The rookie caught the pass in stride and went untouched for a 99-yard touchdown.

2. Bills thin at tight end

The Bills' aren't just dealing with injuries on the offensive line. In fact, the injury bug has caught the tight end position even worse. Scott Chandler (groin) and Tony Moeaki (hamstring) are still out, and Lee Smith missed practice on Thursday with a lower body injury. Luckily, Chris Gragg was able to return Wednesday and should be ready to play Sunday. The second-year tight end was hospitalized with cramps and missed a week of practice.

"It's been going good," Gragg said. "With guys down, I've been getting the opportunity to get a lot of work."

Marrone said he hopes to have Gragg as a full participant in the Hall of Fame Game against the Giants on Sunday.

3. Nickell Robey stands out

After a breakout season as a rookie, Nickell Robey has found himself in the middle of a competition for the Bills' slot cornerback role. On Thursday, Robey stood out, both in team work and one-on-one drills. He's exceptional at changing directions and playing bigger than his size.

The only noticeable negative play from Robey on Thursday was when he was beat down the sideline by Chris Hogan. But the way Hogan has been playing lately, that's nothing for Robey to be ashamed of.

4. T.J. Graham getting more work

Physical talent will get a player an extra opportunity or two. Despite dropping quite a few passes early in training camp, and a few more on Thursday, wide receiver T.J. Graham was getting more significant reps than he's had most of camp.

Graham is among the fastest players on the Bills' roster, so coaches would like to take advantage of that. But the preseason games will likely determine whether Graham cracks the final roster.

5. Competition for short-yardage carries

With the Bills practicing having their back up against their own goal line, there were a few items of note. Considering those carries are generally reserved for a running back who doesn't need to break a big run but just needs to gain positive yardage, it's safe to say the short-yardage back can be counted on.

Fullback Frank Summers got the first carry of the drill, while Anthony Dixon and Fred Jackson handled the other carries. Dixon again looked sharp, showing strong vision between the tackles. Jackson isn't going away, though, so that competition will be worth monitoring during camp.